A plant endophyte Staphylococcus hominis strain MBL_AB63 produces a novel lantibiotic, homicorcin and a position one variant

Here we report a jute endophyte Staphylococcus hominis strain MBL_AB63 isolated from jute seeds which showed promising antimicrobial activity against Staphylococcus aureus SG511 when screening for antimicrobial substances. The whole genome sequence of this strain, annotated using BAGEL4 and antiSMASH 5.0 to predict the gene clusters for antimicrobial substances identified a novel antimicrobial peptide cluster that belongs to the class I lantibiotic group. The predicted lantibiotic (homicorcin) was found to be 82% similar to a reported peptide epicidin 280 having a difference of seven amino acids at several positions of the core peptide. Two distinct peaks obtained at close retention times from a RP-HPLC purified fraction have comparable antimicrobial activities and LC-MS revealed the molecular mass of these peaks to be 3046.5 and 3043.2 Da. The presence of an oxidoreductase (homO) similar to that of epicidin 280- associated eciO or epilancin 15X- associated elxO in the homicorcin gene cluster is predicted to be responsible for the reduction of the first dehydrated residue dehydroalanine (Dha) to 2-hydroxypropionate that causes an increase of 3 Da mass of homicorcin 1. Trypsin digestion of the core peptide and its variant followed by ESI-MS analysis suggests the presence of three ring structures, one in the N-terminal and other two interlocking rings at the C-terminal region that remain undigested. Homicorcin exerts bactericidal activity against susceptible cells by disrupting the integrity of the cytoplasmic membrane through pore formation as observed under FE-SEM.

Identification and characterization of Pseudomonas aeruginosa derived bacteriocin for industrial applications

Drug resistance has become a major threat due to the frequent use of commercial antibiotics and there is an urgent need to combat this problem. Having this in mind, the present research was aimed at developing a novel P. aeruginosa puBac bacteriocin molecule. The bacteriocin was purified by ammonium sulfate precipitation followed by Sepharose FF and Sephadex G15 column purification and the purified bacteriocin has been reported to have the molar mass of 43 kDa. The findings of the optimization showed that 3500 AU/mL of bacteriocin was obtained at 37 °C, 3410 AU/mL of bacteriocin at 6.5 pH and 3780 AU/mL of bacteriocin at 48 h of incubation time. In addition, 3863 AU/mL of bacteriocin activity was obtained with Tween-80 followed by 3789 AU/mL with a concentration of 2% NaCl and 4200 AU/mL for Fe²⁺. PuBac bacteriocin has been shown to have a significant effect on test pathogens. For example, E. coli was found to have 3.6 μM of MIC, followed by Staphylococcus sp. with 6.15 μM of MIC and Bacillus sp. with a 7.5 μM of MIC. The remarkable properties of bacteriocin suggest that it could be used in various pharmaceutical and food industries.

Identification and characterisation of capidermicin, a novel bacteriocin produced by Staphylococcus capitis

One hundred human-derived coagulase negative staphylococci (CoNS) were screened for antimicrobial activity using agar-based deferred antagonism assays with a range of indicator bacteria. Based on the findings of the screen and subsequent well assays with cell free supernatants and whole cell extracts, one strain, designated CIT060, was selected for further investigation. It was identified as Staphylococcus capitis and herein we describe the purification and characterisation of the novel bacteriocin that the strain produces. This bacteriocin which we have named capidermicin was extracted from the cell-free supernatant of S. capitis CIT060 and purified to homogeneity using reversed-phase high performance liquid chromatography (RP-HPLC). Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometric (MS) analysis revealed that the capidermicin peptide has a mass of 5,464 Da. Minimal inhibitory concentration (MIC) experiments showed that capidermicin was active in the micro-molar range against all the Gram-positive bacteria that were tested. Antimicrobial activity was retained over a range of pHs (2–11) and temperatures (10–121°C x 15 mins). The draft genome sequence of S. capitis CIT060 was determined and the genes predicted to be involved in the biosynthesis of capidermicin were identified. These genes included the predicted capidermicin precursor gene, and genes that are predicted to encode a membrane transporter, an immunity protein and a transcriptional regulator. Homology searches suggest that capidermicin is a novel member of the family of class II leaderless bacteriocins.

Bacteriocin Occurrence and Activity in Escherichia coli Isolated from Bovines and Wastewater

The increasing prevalence of antimicrobial resistant (AMR) E. coli and related Enterobacteriaceae is a serious problem necessitating new mitigation strategies and antimicrobial agents. Bacteriocins, functionally diverse toxins produced by most microbes, have long been studied for their antimicrobial potential. Bacteriocins have once again received attention for their role as probiotic traits that could mitigate pathogen burden and AMR bacteria in livestock. Here, bacteriocins were identified by activity screening and whole-genome sequencing of bacteriocin-producers capable of inhibiting bovine and wastewater E. coli isolates enriched for resistance to cephalosporins. Producers were tested for activity against shiga toxin-producing E. coli (STEC), AMR E. coli, and related enteric pathogens. Multiple bacteriocins were found in 14 out of 90 E. coli isolates tested. Based on alignment within BACTIBASE, colicins M, B, R, Ia, Ib, S4, E1, E2, and microcins V, J25, and H47, encoded by identical, variant, or truncated genes were identified. Although some bacteriocin-producers exhibited activity against AMR and STEC E. coli in agar-based assays, most did not. Despite this idiosyncrasy, liquid co-cultures of all bacteriocinogenic isolates with luciferase-expressing generic (K12) or STEC E. coli (EDL933) resulted in inhibited growth or reduced viability. These abundant toxins may have real potential as next-generation control strategies in livestock production systems but separating the bacteriocin from its immunity gene may be necessary for such a strategy to be effective.

Exploring bioactive peptides from bacterial secretomes using PepSAVI-MS: identification and characterization of Bac-21 from Enterococcus faecalis pPD1

As current methods for antibiotic drug discovery are being outpaced by the rise of antimicrobial resistance, new methods and innovative technologies are necessary to replenish our dwindling arsenal of antimicrobial agents. To this end, we developed the PepSAVI-MS pipeline to expedite the search for natural product bioactive peptides. Herein we demonstrate expansion of PepSAVI-MS for the discovery of bacterial-sourced bioactive peptides through identification of the bacteriocin Bac-21 from Enterococcus faecalis pPD1. Minor pipeline modifications including implementation of bacteria-infused agar diffusion assays and optional digestion of peptide libraries highlight the versatility and wide adaptability of the PepSAVI-MS pipeline. Additionally, we have experimentally validated the primary protein sequence of the active, mature Bac-21 peptide for the first time and have confirmed its identity with respect to primary sequence and post-translational processing. Successful application of PepSAVI-MS to bacterial secretomes as demonstrated herein establishes proof-of-principle for use in novel microbial bioactive peptide discovery.

A Multibacteriocin Cheese Starter System, Comprising Nisin and Lacticin 3147 in Lactococcus lactis, in Combination with Plantaricin from Lactobacillus plantarum

Functional starter cultures demonstrating superior technological and food safety properties are advantageous to the food fermentation industry. We evaluated the efficacies of single- and double-bacteriocin-producing starters of Lactococcus lactis capable of producing the class I bacteriocins nisin A and/or lacticin 3147 in terms of starter performance. Single producers were generated by mobilizing the conjugative bacteriophage resistance plasmid pMRC01, carrying lacticin genetic determinants, or the conjugative transposon Tn5276, carrying nisin genetic determinants, to the commercial starter L. lactis CSK2775. The effect of bacteriocin coproduction was examined by superimposing pMRC01 into the newly constructed nisin transconjugant. Transconjugants were improved with regard to antimicrobial activity and bacteriophage insensitivity compared to the recipient strain, and the double producer was immune to both bacteriocins. Bacteriocin production in the starter was stable, although the recipient strain proved to be a more efficient acidifier than transconjugant derivatives. Overall, combinations of class I bacteriocins (the double producer or a combination of single producers) proved to be as effective as individual bacteriocins for controlling Listeria innocua growth in laboratory-scale cheeses. However, using the double producer in combination with the class II bacteriocin producer Lactobacillus plantarum or using the lacticin producer with the class II producer proved to be most effective for reducing bacterial load. As emergence of bacteriocin tolerance was reduced 10-fold in the presence of nisin and lacticin, we suggest that the double producer in conjunction with the class II producer could serve as a protective culture providing a food-grade, multihurdle approach to control pathogenic growth in a variety of industrial applications.IMPORTANCE We generated a suite of single- and double-bacteriocin-producing starter cultures capable of generating the class I bacteriocin lacticin 3147 or nisin or both bacteriocins simultaneously via conjugation. The transconjugants exhibited improved bacteriophage resistance and antimicrobial activity. The single producers proved to be as effective as the double-bacteriocin producer at reducing Listeria numbers in laboratory-scale cheese. However, combining the double producer or the lacticin-producing starter with a class II bacteriocin producer, Lactobacillus plantarum LMG P-26358, proved to be most effective at reducing Listeria numbers and was significantly better than a combination of the three bacteriocin-producing strains, as the double producer is not inhibited by either of the class I bacteriocins. Since the simultaneous use of lacticin and nisin should reduce the emergence of bacteriocin-tolerant derivatives, this study suggests that a protective starter system produced by bacteriocin stacking is a worthwhile multihurdle approach for food safety applications.

Improved lanthipeptide detection and prediction for antiSMASH

Lanthipeptides are a class of ribosomally synthesised and post-translationally modified peptide (RiPP) natural products from the bacterial secondary metabolism. Their name is derived from the characteristic lanthionine or methyl-lanthionine residues contained in the processed peptide. Lanthipeptides that possess an antibacterial activity are called lantibiotics. Whereas multiple tools exist to identify lanthipeptide gene clusters from genomic data, no programs are available to predict the post-translational modifications of lanthipeptides, such as the proteolytic cleavage of the leader peptide part or tailoring modifications based on the analysis of the gene cluster sequence. antiSMASH is a software pipeline for the identification of secondary metabolite biosynthetic clusters from genomic input and the prediction of products produced by the identified clusters. Here we present a novel antiSMASH module using a rule-based approach to combine signature motifs for biosynthetic enzymes and lanthipeptide-specific cleavage site motifs to identify lanthipeptide clusters in genomic data, assign the specific lanthipeptide class, predict prepeptide cleavage, tailoring reactions, and the processed molecular weight of the mature peptide products.

Bioavailability of the anti-clostridial bacteriocin thuricin CD in gastrointestinal tract

Thuricin CD is a two component narrow spectrum bacteriocin comprising two peptides with targeted activity against Clostridium difficile. This study examined the bioavailability of thuricin with a view to developing it as an effective antimicrobial against intestinal infection. One of the peptides, Trn-β, was found to be degraded by the gastric enzymes pepsin and α-chymotrypsin both in vitro and in vivo, whereas Trn-α was resistant to digestion by these enzymes and hence was detected in the intestinal porcine digesta following oral ingestion by pigs. In order to determine if spores of the producing organism Bacillus thuringiensis DPC 6431 could be used to deliver the bacteriocin to the gut, spores were fed to 30 mice (approx. 10(8)-2×10(8) per animal) and their germination, growth and production of thuricin in the gastrointestinal tract (GIT) of the animals was monitored. Almost 99 % of the spores delivered to the GIT were excreted in the first 24 h and neither Trn-α nor Trn-β was detected in the gut or faecal samples of the test mice, indicating that ingestion of B. thuringiensis spores may not be a suitable vehicle for the delivery of thuricin CD. When thuricin CD was delivered rectally to mice (n = 40) and C. difficile shedding monitored at 1, 6, 12 and 24 h post-treatment, there was a >95 % (>1.5 log units) reduction of C. difficile 027 in the colon contents of infected mice (n = 10) 1 h post-treatment compared with the control group (n = 10; P<0.001). Furthermore, 6 h post-treatment there was a further 1.5 log reduction in C. difficile numbers (n = 10) relative to the control group (n = 10; P<0.05). These results would suggest that rectal administration of thuricin may be a promising mode of delivery of thuricin CD to the colon.

[Detection of uncultivable bacteria forms in probiotic lyophilized preparations]

AIM

Detection of viable but uncultivable forms among lyophilized cells of commercial probiotics.

MATERIALS AND METHODS

9 series of probiotic preparations (colibacterin, bificol, bifidumbacterin, bifiform) with expired (up to 30 years of storage) or valid shelf life were objects of the study. Total quantity of the bacteria was calculated under the microscope in Goryaev chamber, the number of viable cells was determined in luminescence microscope after staining by an array of fluorescent dyes, the quantity of CFU/ml was evaluated by method of seeding into the respective solid or semi-liquid cultivation medium.

RESULTS

Juxtaposition of the specified parameter values allowed to establish that in lyophilized preparations of colibacterin with expired shelf life the amount of viable but not forming colonies (uncultivable forms) cells varied from 4.13 to 99.73% depending on date of production. For bifidumbacterin with unexpired shelf life live cells constituted 95.45 and 70.73%. The amount of viable bifidobacteria forming colonies was on the level of 100 and 50%, respectively. In bifidopreparations micro colonies that may possibly be formed spontaneously by awakened uncultivable forms were noted. A possibility of growth stimulation of these cells by 1 and 10% aminopeptide was shown.

CONCLUSION

The presence of uncultivable forms in lyophilized preparations of probiotics was proven experimentally.

Partial characterization of bacteriocins produced by two Lactobacilus strains with probiotic properties

The probiotic characteristics of Lactobacillus brevis BG18 and Lb. plantarum BG33, isolated from traditional Turkish Tulum cheese were assessed. These two bacteriocinproducer strains exhibited good probiotic characteristics such as resistance in media containing 0.3% bile salt, pepsin (3 mg mL⁻¹), and pancreatine (1 mg mL⁻¹) as well as acid resistance at pH 2. They were also adhered to Caco-2 epithelial cells in a manner comparable to Escherichia coli LMG3083 (ETEC) and Salmonella Typhimurium SL1344. The strains produced a heat-stable antimicrobial compound that was shown to be proteinaceous in nature, and therefore, referred to as bacteriocins. The bacteriocins were able to inhibit growth of a number grampositive bacteria such as Listeria monocytogenes, Clostridium botulinum, Staphylococcus aureus and Bacillus cereus. Tricine-SDS-PAGE of the active fraction resulted in single bands with estimated molecular masses of 2.5 kDA and 2.7 kDA for Lb. brevis BG18 and Lb. plantarum BG33 bacteriocins, respectively.

Activity assay for nisin-like acidic bacteriocins using an optimal pH-conditioned gel matrix

A new zymography for detecting nisin-like acidic bacteriocins was developed using a tricine-sodium dodecyl sulfate (SDS) gel and an acidic gel matrix (pH 4.0). After electrophoresis, proteins in the tricine gel were electrotransferred to an optimal pH-conditioned gel matrix (OP-CGM). The OP-CGM was overlaid with indicator cells (Bacillus cereus) embedded in nutrient broth soft agar (0.8%, w/v). Antibacterial activity shown as a growth inhibition using B. cereus was detected at approximately 3.8kDa. Because nisin is unstable in buffers at pH values over 6.0, the common electrophoretic systems, SDS-polyacrylamide gel electrophoresis and tricine gel, are not suitable for detection of nisin-like acidic bacteriocins.

Diverse Antibacterial activity of Pectobacterium carotovorum subsp.carotovorum isolated in Korea

Fifty-four Pectobacterium carotovorum subsp. carotovorum strains isolated in Korea were characterized by a spectrum of antibacterial activities against 7 indicator strains chosen to represent various regions and host plants. All P. carotovorum subsp. carotovorum isolates tested could be grouped into 4 classes depending on the pattern of antibacterial substance production. All tested strains had DNA fragment(s) homologous to the genes encoding carotovoricin and 21 of them had genes homologous to DNA invertase. Sixteen strains had genes homologous to the genes encoding carocin S1. Several isolates produced antibacterial substances active against strains in Brenneria, Pantoea, and Pectobacterium genera that belonged formerly to the genus Erwinia. Strains in Pseudomonas or Xanthomonas sp. were not sensitive to the antibacterial substances produced by P. carotovorum subsp. carotovorum, except for X. albilineans that was sensitive to antibacterial substances produced by most strains in P. carotovorum subsp. carotovorum and P. betavasculorum KACC10056. These results demonstrated the diverse patterns of antibacterial substance production and the possibility of the existence of new antibacterial substance(s) produced by P. carotovorum subsp. carotovorum isolated in Korea.

Evidence for probiotic potential of a capsular-producing Streptococcus thermophilus CHCC 3534 strain

The purpose of this research was to evaluate the probiotic potential of an capsulated Streptococcus thermophilus CHCC 3534 strain. The strain tolerates 0.4% oxgall (bile) and was sufficiently resistant to pH as low as 2.5 for 3 hours of exposure. The strain demonstrated high adherence to human intestinal mucus, and showed unique resistance to different antibiotics. Crude extracts ofS. thermophilus CHCC 3534 contained a diffusible antimicrobial compound "bacteriocin" with a broad spectrum that inhibited the growth of closely related lactic acid bacteria and a number of food spoilage bacteria including Salmonella typhimurium and Staphylococcus aureus. The bacteriocin was heat stable, resistant to pH, inactivated by proteolytic enzymes, and resistant to a-amylase and lipase. A SDS-PAGE analysis of the partially purified bacteriocin revealed one component with a molecular weight ranging from 14.4 to 18.4 kDa. The strain may have industrial significance and represents an interesting candidate for use in biopreservation, probiotic food formulations and in the control of spoilage caused by food borne pathogens.

Combined physico-chemical treatments based on enterocin AS-48 for inactivation of Gram-negative bacteria in soybean sprouts

Enterocin AS-48 was tested for decontamination of soybean sprouts against Gram-negative bacteria. Although treatment with bacteriocin alone had no effect on Salmonella enterica, a synergistic antimicrobial effect was detected at pH 9.0 and in combination with moderate heat treatment. Greatest inactivation was achieved for sprouts heated for 5 min at 65 degrees C in an alkaline (pH 9.0) enterocin AS-48 solution of 25 microg/ml. Bactericidal activity against S. enterica increased greatly when enterocin AS-48 was used in washing solutions in combination with several chemical compounds: EDTA, lactic acid, peracetic acid, polyphosphoric acid, sodium hypochlorite, hexadecylpyridinium chloride, propyl-p-hydroxybenzoate, and hydrocinnamic acid. The combined treatment of enterocin AS-48 and polyphosphoric acid was tested against several other Gram-negative bacteria inoculated on sprouts. The bacteria tested showed great differences in sensitivity to polyphosphoric acid, but synergism with enterocin AS-48 was confirmed in all cases. Combinations of enterocin AS-48 (25 microg/ml) and polyphosphoric acid in a concentration range of 0.1 to 2.0% significantly reduced or inhibited growth of the populations of S. enterica, Escherichia coli O157:H7, Shigella spp., Enterobacter aerogenes, Yersinia enterocolitica, Aeromonas hydrophila and Pseudomonas fluorescens in sprout samples stored at 6 degrees C and 15 degrees C. The combined treatment could therefore be applied to reduce the risks of Gram-negative pathogenic as well as spoilage bacteria on sprouts.

Detection of pediocin PA-1 in food matrices using specific polyclonal antibodies

Pediocin PA-1 was conjugated with keyhole limpet hemocyanin (KLH) and used to immunize rabbits and mice for the production of polyclonal (PAb) and monoclonal (MAb) antibodies. Titers of PAb and MAb of about 4.7 and 2.9 were obtained after three and six immunizations, respectively. An enzyme linked immunosorbent assay (ELISA) was developed for the detection and quantification of pediocin.

A rapid and accurate 3-(4,5-dimethyl thiazol-2-yl)-2,5-diphenyl tetrazolium bromide colorimetric assay for quantification of bacteriocins with nisin as an example

The objective of this study is to propose a more accurate and faster MTT [3-(4,5-dimethyl thiazol-2-yl)-2,5-diphenyl tetrazolium bromide] colorimetric assay (MCA) for quantitative measurement of polypeptide bacteriocins in solutions with nisin as an example. After an initial incubation of nisin and indicator bacterium Micrococcus luteus NCIB 8166 in tubes, MTT was added for another incubation period. After that, nisin was quantified by estimating the number of viable bacteria based on measuring the amount of purple formazan produced by cleavage of yellow tetrazolium salt MTT. Then MCA was compared to a standard agar diffusion assay (ADA). The results suggested a high correlation coefficient (r(2)=0.975+/-0.004) between optical density (OD) and the inhibitory effect of nisin on a bacterial strain Micrococcus luteus NCIB 8166 at a range of 0.125-32 IU/ml. The MCA described in this study was very quick. Quantification of nisin took only 7-8 h and the detection limit was at the level of 0.125 IU/ml when compared to 12 IU/ml and 24-28 h for ADA. The MCA provides an accurate and rapid method for quantification of nisin in solutions and is expected to be used for quantification of other antimicrobial substances.

A new rapid fluorogenic method for measuring bacteriocin activity

We describe a novel bacteriocin screening assay based on fluorescence emitted by berberine following its influx into compromised cells. This technique showed agreement with the conventional well-diffusion method, and results can be obtained within one hour. This assay could facilitate the rapid identification of bacteriocinogenic bacterial isolates.

Development and application of a microtiter plate-based autoinduction bioassay for detection of the lantibiotic subtilin

Production of the lantibiotic subtilin in Bacillus subtilis ATCC 6633 is regulated in a quorum sensing-like mechanism with subtilin acting as autoinducer and signal transduction via the subtilin-specific two-component regulation system SpaRK. Here, we report the construction and application of a subtilin reporter strain in which subtilin induced lacZ gene expression in a B. subtilis ATCC 6633 spaS gene deletion mutant is monitored and visualized by the beta-galactosidase in a chromogenic plate assay. A quantitative microtiter plate subtilin bioassay was developed and optimized. Maximal sensitivity of the system was achieved after 6 h of incubation of the reporter strain together with subtilin in a medium containing 300 mM NaCl. This sensitive and unsusceptible method was applied to identify subtilin producing B. subtilis wild type strains from both, culture collections and soil samples. The B. subtilis lantibiotic ericin S with four amino acid exchanges compared to subtilin induces the subtilin reporter strain, in contrast to the structurally closely related Lactococcus lactis lantibiotic nisin. These observations suggest a certain substrate specificity of the histidine kinase SpaK, which however, also would allow the identification of subtilin-isoform producing microorganisms.

The tomato pathogen Clavibacter michiganensis ssp. michiganensis: producer of several antimicrobial substances

AIM

To purify and analyse antimicrobial substances produced by the tomato pathogen Clavibacter michiganensis ssp. michiganensis (Cmm), with potential application in control of Clavibacter michiganensis ssp. sepedonicus (Cms), the causal agent of bacterial ring rot of potato.

METHODS AND RESULTS

After selection of a suitable producer and indicator strain, antimicrobial compounds were isolated using chromatographic techniques. The resulting preparations were analysed with respect to heat and protease sensitivity, amino acid composition, amino acid sequence and mass. Using this procedure we discovered one post-translationally modified 2145 Da peptide bacteriocin, one 14 kDa antimicrobial protein as well as low molecular weight (<1000 Da) antimicrobial compounds, putatively belonging to the tunicamycin family.

CONCLUSIONS

Clavibacter michiganensis ssp. michiganensis produces various antibacterial substances that are active against Cms.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study describes the first attempt to characterize antimicrobial substances from Cmm at the molecular level. This is an important step towards investigation of the possible use of these compounds to control the potato ring rot pathogen.

Exoproducts of the Escherichia coli strain H22 inhibiting some enteric pathogens both in vitro and in vivo

AIMS

The antagonistic activity of the Escherichia coli strain H22 against enteric bacteria was studied both in vitro and in vivo.

METHODS AND RESULTS

In vitro, bacterial strains belonging to seven of nine genera of the family Enterobacteriaceae (Enterobacter, Escherichia, Klebsiella, Morganella, Salmonella, Shigella and Yersinia) were inhibited by the strain H22. Six days after simultaneous oral inoculation in germ-free mice, E. coli strain H22 reduced the faecal population of Shigella flexneri 4 to undetectable levels (P < 0.05). In ex vivo assay, inhibitory zones against Sh. flexneri 4 were observed around faecal samples from mice inoculated with E. coli strain H22. The in vitro inhibition of Sh. flexneri 4 was shown to be mediated by microcin C7. In addition to microcin C7, strain H22 was shown to produce aerobactin, new variants of colicins E1 and Ib, and bacteriophage particles with morphology similar to the phages of the family Myoviridae.

CONCLUSIONS

Altogether, the properties of E. coli H22, observed both under in vitro and in vivo conditions, suggest its potential use as a probiotic strain for livestock and humans.

SIGNIFICANCE AND IMPACT OF THE STUDY

The strain H22 was shown to produce several antimicrobial compounds with inhibitory capabilities against pathogenic or potentially pathogenic enterobacteria.

Isolation and preliminary characterization of a bacteriocin produced by Lactobacillus plantarum N014 isolated from nham, a traditional Thai fermented pork

Lactobacillus plantarum N014 was isolated from nham, a traditional Thai fermented pork, and exhibited antimicrobial activity against Listeria monocytogenes. Its bacteriocin had a broad inhibitory spectrum toward both gram-positive and gram-negative bacteria. The bacteriocin activity was sensitive to all proteolytic enzymes used in this study, including papain, pepsin, pronase E, proteinase K, and trypsin, but was resistant to the other enzymes, such as alpha-amylase, lipase A, and lysozyme. Furthermore, activity was stable over various heat treatments and pH values. The bacteriocin exerted a bacteriolytic mode of action. It was produced during the exponential growth phase and reached its highest level as producer cells entered the stationary phase. Adsorption of the bacteriocin onto producer cells was pH-dependent. No bacteriocin adsorption was detected at pH 1 to 3, whereas 100% bacteriocin adsorption was found at pH 7. Plasmid isolation revealed that L. plantarum N014 contained no plasmids. From Tricine-sodium dodecyl sulfate-polyacrylamide gel electrophoresis and growth inhibition testing against L. monocytogenes, the estimated molecular mass of L. plantarum N014 bacteriocin was 8 kDa.

Bac 32, a novel bacteriocin widely disseminated among clinical isolates of Enterococcus faecium

A total of 636 vancomycin-resistant Enterococcus faecium (VRE) isolates that had been obtained between 1994 and 1999 from the Medical School Hospital of the University of Michigan, Ann Arbor, were tested for bacteriocin production. Two hundred seventy-seven (44%) of the strains were bacteriocinogenic; and 193 of these exhibited activity against Enterococcus faecium, Enterococcus hirae, and Enterococcus durans. Strain VRE200 harbors the highly efficient conjugative gentamicin resistance plasmid pG200 (70 kb) and bacteriocin plasmid pTI1 (12.5 kb). The bacteriocin encoded on pTI1 was designated bacteriocin 32 (Bac 32). Bacteriocin 32 was active against E. faecium, E. hirae, and E. durans but showed no activity against Listeria monocytogenes. The Bac 32 genetic locus consists of a bacteriocin gene (bacA) and an immunity gene (bacB). Neither of these genes showed significant homology to any known bacteriocin determinants. The deduced bacA product is 89 amino acids in length, with a putative signal peptide of 19 amino acids at the N terminus. The bacB gene encodes a deduced 55-amino-acid protein without a signal sequence. One hundred eighty-nine strains (97.9%) of the 193 strains with activity against the 3 test enterococcal strains gave rise to the expected specific PCR product with a primer specific for bacA, indicating that there is a high incidence of Bac 32 production among VRE clinical isolates. Data from Southern analyses of plasmid DNA from 189 of the Bac 32-producing strains with a plasmid pTI1-specific probe suggested that 137 (72.5%) of the strains harbored a pTI1-type plasmid. Bac 32 or Bac 32-type bacteriocin activity and the determinant genes were also identified in 22 (39.3%) of a total of 56 vancomycin-sensitive E. faecium clinical isolates, which suggests that this bacteriocin is widely disseminated among E. faecium strains.

Production of the lantibiotic salivaricin A and its variants by oral streptococci and use of a specific induction assay to detect their presence in human saliva

Salivaricin A (SalA), the first Streptococcus salivarius lantibiotic to be characterized, appears to be inhibitory to most Streptococcus pyogenes strains. A variant of the SalA structural gene (salA1) is present in more than 90% of S. pyogenes strains, but only strains of M serotype 4 and T pattern 4 produce the biologically active peptide. The present study identifies four additional variants (salA2 to salA5) of the SalA structural gene and demonstrates that each of the corresponding inhibitory peptides (SalA2 to SalA5) is produced in vitro. These variants appear to be similar to SalA and SalA1 in their inhibitory activity against Micrococcus luteus and in their ability to act as inducers of SalA production. It had previously been shown that S. pyogenes strain SF370 had a deletion (of approximately 2.5 kb) in the salM and salT genes of the salA1 locus. In the present study, several additional characteristic deletions within the salA1 loci were identified. S. pyogenes strains of the same M serotype all share the same salA1 locus structure. Since S. salivarius is a predominant member of the normal oral flora of healthy humans, strains producing anti-S. pyogenes lantibiotics, such as SalA, may have excellent potential for use as oral probiotics. In the present study, we have used a highly specific SalA induction system to directly detect the presence of SalA in the saliva of humans who either naturally harbor populations of SalA-producing S. salivarius or who have been colonized with the SalA2-producing probiotic S. salivarius K12.

Characterization of bacteriocins from twoLactococcus lactis subsp.lactis isolates

In this study, bacteriocins from two Lactococcus lactis subsp. lactis isolates from raw milk samples in Turkey designated OC1 and OC2, respectively, were characterized and identified. The activity spectra of the bacteriocins were determined by using different indicator bacteria including Listeria, Bacillus and Staphylococcus spp. Bacteriocins were tested for their sensitivity to different enzymes, heat treatments and pH values. Loss of bacteriocin activities after alpha-amylase treatment suggested that they form aggregates with carbohydrates. Molecular masses of the purified bacteriocins were determined by SDS-PAGE. PCR amplification was carried out with specific primers for the detection of their structural genes. As a result of these studies, the two bacteriocins were characterized as nisin and lacticin 481, respectively. Examination of plasmid contents of the isolates and the results of plasmid curing and conjugation experiments showed that in L. lactis subsp. lactis OC1 strain the 39.7-kb plasmid is responsible for nisin production, lactose fermentation and proteolytic activity, whereas the 16.0-kb plasmid is responsible for lacticin 481 production and lactose fermentation in L. lactis subsp. lactis OC2 strain.

Phage tail-like (high-molecular-weight) bacteriocins of Budvicia aquatica and Pragia fontium (Enterobacteriaceae)

Electron microscopic analysis of contractile phage tail-like bacteriocins of three Pragia fontium strains and one Budvicia aquatica strain was performed. Fonticin and aquaticin are remarkably heat sensitive but trypsin resistant. Simultaneous production of contractile and flexible phage tail-like bacteriocins in the P. fontium 64613 strain is shown for the first time.

Does double electron capture lead to the formation of biradicals? An ECD-SORI-CID study on lacticin 481

We studied lacticin 481, a small lantibiotic with three lanthionine bridges, by electron capture dissociation (ECD) in a Fourier transform ion cyclotron resonance (FTICR) mass spectrometer. Following electron capture, very little fragmentation was observed, but species formed by nondissociative single and multiple electron capture were abundant. Ions formed by double electron capture were subjected to sustained off resonance irradiation collision induced dissociation (SORI-CID) to determine whether stable biradicals were formed. In the SORI-CID spectra of the ions formed by double electron capture, some, but minor, H* radical loss was observed, which was not observed at all for regularly protonated ions. A small part of the ions formed by double electron capture are thus long-lived biradicals. Apart from the observed H* loss, the SORI-CID spectra of ions that captured two electrons was similar to that of regularly protonated ions and quite different from the SORI-CID spectra of radical ions formed by single electron capture. This implies that recombination of the two radical sites is the dominant process in biradical lacticin 481 ions, at least on the time scale of our SORI-CID experiments.

A novel bacteriocin-like substance (BLIS) from a pathogenic strain of Vibrio harveyi

Inter-strain and inter-species inhibition mediated by a bacteriocin-like inhibitory substance (BLIS) from a pathogenic Vibrio harveyi strain VIB 571 was demonstrated against four isolates of the same species, and one culture each of a Vibrio sp., Vibrio fischeri, Vibrio gazogenes and Vibrio parahaemolyticus. The crude BLIS, which was obtained by ammonium-sulphate precipitation of the cell-free supernatant of a 72 h broth culture of strain VIB 571, was inactivated by lipase, proteinase K, pepsin, trypsin, pronase E, SDS and incubation at ≥60 °C for 10 min. The activity was stable between pH 2–11 for at least 5 h. Anion-exchange chromatography, gel filtration, SDS-PAGE and two-dimensional gel electrophoresis revealed the presence of a single major peak, comprising a protein with a pI of ∼5·4 and a molecular mass of ∼32 kDa. The N-terminal amino acid sequence of the protein comprised Asp-Glu-Tyr-Ile-Ser-X-Asn-Lys-X-Ser-Ser-Ala-Asp-Ile (with X representing cysteine or modified amino acid residues). A similarity search based on the matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) generated peptide masses and the N-terminal sequence did not yield any significant matches.

Purification and characterization of pertucin produced by Pseudomonas pertucinogena

Pertucin, a bacteriocin active against phase I organisms of Bordetella pertussis, was extracted from Pseudomonas pertucinogena, strain 190 or 6627, by freezing and thawing of bacteria-free agar medium and was purified by ammonium sulfate fractionation, dialysis, zinc chloride precipitation, and polyacrylamide gel electrophoresis. The specific activity of purified pertucin was approximately 80 times that of the crude extract. The purified pertucin preparation was homogeneous on ultracentrifugal analysis and polyacrylamide gel electrophoresis, and was found to be composed of protein (80%) and carbohydrate (20%), the latter assumed not to be bound covalently to the protein. Neither nucleic acids nor lipids were demonstrated. N-terminal analysis by dansylation revealed only methionine in strain 190 and only glycine in strain 6627. The isoelectric point was found to be 4.8, and the molecular weight was estimated to be 31,500. Amino acid analysis of the protein moiety demonstrated that it contained all of the common amino acids with somewhat more of the hydrophilic amino acids. With respect to thermostability, pH stability, and effects of metal ions and various buffers, pertucin behaves like a protein and is stable in 0.05 M tris(hydroxymethyl)aminomethane buffer, pH 8.0, containing 0.01 M Ca(2+).

Purification and characterization of syringacin 4-A, a bacteriocin from pseudomonas syringae 4-A

Syringacin 4-A, a bacteriocin produced by Pseudomonas syrinagae 4-A, was obtained by induction with ultraviolet irradiation or mitomycin C. Approximately 1,000-fold purification of the bacteriocin was achieved by manganous chloride precipitation, differential centrifugation, and chromatography on hydroxyapatite columns. The purified syngacin was homogeneous on hydroxyapatite columns and sucrose density gradients; it also sedimented as a single entity in the analytical ultracentrifuge. The buoyant density of purified syringacin in cesium chloride was 1.294 g/ml. The sedimentation coefficient was calculated as 120S, and the diffusion coefficient was 6.49 x 10(-8) cm(2)/s. The molecular weight was calculated as 1.6 x 10(7) from physical data and 1.7 x 10(7) from biological data. The syringacin was composed of about 88.4% protein, 8.5% arabinose, 2.2% galacturonic acid, and 0.7% glucosamine. Amino acid analysis indicated a predominance of leucine (12.1%), aspartic acid (12.2%), and glutamic acid (12.7%). The ultraviolet spectrum showed a maximum absorbance peak at 276 nm. The syringacin was heat and alcohol sensitive, but resistant to trypsin, chymotrypsin, carboxypeptidase, Pronase, protease, lysozyme, steapsin, deoxyribonuclease, and ribonuclease. Maximum pH stability was between 5 and 8. Crude bacteriocin was stable at room temperature for at least a year, and purified material was stable for at least 3 months at 4 C.

Purification and characterisation of acidocin D20079, a bacteriocin produced by Lactobacillus acidophilus DSM 20079

Bacteriocins are natural antimicrobial agents produced by food fermentative bacteria. Lactobacillus acidophilus DSM 20079 produces a small bacteriocin, with a molecular mass of 6.6 kDa, designated acidocin D20079. This antimicrobial peptide was extremely heat-stable (30 min at 121 degrees C) and was active over a wide pH range. It was found to be sensitive to proteolytic enzymes (trypsin, ficin, pepsin, papain, and proteinase K). Acidocin D20079 has a narrow inhibitory spectrum restricted to the genus Lactobacillus which includes L. sakei NCDO 2714, an organism known to cause anaerobic spoilage of vacuum-packaged meat. Maximum production of acidocin D20079 in MRS broth was detected at pH 6.0, and the peptide was purified by ammonium sulphate precipitation followed by sequential cation exchange and hydrophobic interaction chromatography. Purified acidocin D20079 spontaneously formed spherulite crystals during dialysis. As the N-terminus was found to be blocked for sequencing, matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry was used to determine a partial sequence, and the molecular mass of the bacteriocin in the formed crystals (6.6 kDa). Estimates of the molecular weight of the partially purified peptide, using tricine-SDS-PAGE, in which bacteriocin activity was confirmed by overlayer techniques were in accordance with this value.

Antilisterial activity of lactic acid bacteria isolated from rigouta, a traditional Tunisian cheese

AIMS

Screening for lactic acid bacteria (LAB) producing bacteriocins and other antimicrobial compounds is of a great significance for the dairy industry to improve food safety.

METHODS AND RESULTS

Six-hundred strains of LAB isolated from 'rigouta', a Tunisian fermented cheese, were tested for antilisterial activity. Eight bacteriocinogenic strains were selected and analysed. Seven of these strains were identified as Lactococcus lactis and produced nisin Z as demonstrated by mass spectrometry analysis of the purified antibacterial compound. Polymerase chain reaction experiments using nisin gene-specific primers confirmed the presence of nisin operon. Plasmid profiles analysis suggests the presence of, at least, three different strains in this group. MMT05, the eighth strain of this antilisterial collection was identified, at molecular level, as Enterococcus faecalis. The purified bacteriocin produced by this strain showed a molecular mass of 10 201.33 +/- 0.85 Da. This new member of class III bacteriocins was termed enterocin MMT05.

CONCLUSIONS

Seven lactococcal strains producing nisin Z were selected and could be useful as bio-preservative starter cultures. Additional experiments are needed to evaluate the promising strain MMT05 as bio-preservative as Enterococci could exert detrimental or beneficial role in foods.

SIGNIFICANCE AND IMPACT OF THE STUDY

Only a few antibacterial strains isolated from traditional African dairy products were described. The new eight strains described herein contribute to the knowledge of this poorly studied environment and constitute promising strains for fermented food safety.

Molecular Mechanism of Transcription Inhibition by Peptide Antibiotic Microcin J25

21 amino acid peptide Microcin J25 (MccJ25) inhibits transcription by bacterial RNA polymerase (RNAP). MccJ25-resistance mutations cluster in the RNAP secondary channel through which incoming NTP substrates are thought to reach the catalytic center and the 3' end of the nascent RNA is likely to thread in backtracked transcription complexes. The secondary channel also accepts transcript cleavage factors GreA and GreB. Here, we demonstrate that MccJ25 inhibits GreA/GreB-dependent transcript cleavage, impedes formation of backtracked complexes, and can be crosslinked to the 3'-end of the nascent RNA in elongation complexes. These results place the MccJ25 binding site within the secondary channel. Moreover, single-molecule assays reveal that MccJ25 binding to a transcribing RNAP temporarily stops transcript elongation but has no effect on the elongation velocity between pauses. Kinetic analysis of single-molecule data allows us to put forward a model of transcription inhibition by MccJ25 that envisions the complete occlusion of the secondary channel by bound inhibitor.

Meat-Model System Development for Antibacterial Activity Determination

Bacteriocins are antibacterial substances produced by many different bacterial species. Although the bacteriocins form a heterogenous group with respect to production of bacteria, antibacterial spectrum, mode of action, and chemical properties, they are by definition proteinaceous compounds that are bactericidal toward organisms taxonomically close to the producer. The ability of lactic acid bacteria (LAB) to compete and finally dominate in mixed fermentations has been attributed to the production of several antimicrobial metabolites such as organic acids, carbon dioxide, hydrogen peroxide, diacetyl, and bacteriocins. The antimicrobial activities of the LAB have long been known, but their bacteriocins have received limited attention until recently. Numerous strains of lactic acid bacteria associated with food systems are capable of producing bacteriocins, or antibacterial proteins with activity against foodborne pathogens and contaminants. Recently, considerable enphasis has been placed on the physicochemical, biochemical, and genetic characterization of these proteins. Many methods for the detection of bacteriocin production as well as the determination of the potency of bacteriocin preparations have been described. All the usual techniques are based on the fact that bacteriocins can diffuse in solid or semisolid culture media, which are subsequently inoculated with a suitable indicator strain. This method has long been shown to have a good perfomance in the characterization of new bacteriocins. Although results obtained from broth systems show that bacteriocins inhibit target organisms, applied studies must be performed to confirm their effectiveness in food. As many lactic acid bacteria associated with meat products were described to be important natural bacteriocin producers, it has been necessary to assay their inhibitory efficacy in meat or meat products. Because of the complexity of these kinds of foods a simplified meat-model system was developed to determine the inhibitory activity of a bacteriocin.

A rapid turbidometric microplate bioassay for accurate quantification of lactic acid bacteria bacteriocins

A 1 day turbidometric microplate bioassay (TMB) was developed for the rapid, accurate and precise quantification of lactic acid bacteria (LAB) bacteriocins (nisin Z and pediocin PA-1). Parameters such as the concentration of the indicator strains and the incubation time were optimized for each bacteriocin. A high correlation coefficient (r(2)=0.992+/-0.004) was obtained for the exponential regression in the nisin Z concentration range of 20-120 ng/ml with 1 x 10(7) CFU indicator strain (Pediococcus acidilactici UL5) and an incubation time of 3 h. Using these parameters, the detection limit was estimated at 80 ng/ml (3.2 IU/ml), compared to 300 ng/ml for the agar diffusion assay (ADA). High precision (<7%) and accuracy (10%) were obtained for all nisin Z concentrations tested. Similar results were obtained with pediocin PA-1 with r(2)=0.993+/-0.005, a precision (8.2%) and an accuracy lower than 15%.

Immunodetection of the bacteriocin lacticin RM: analysis of the influence of temperature and Tween 80 on its expression and activity

Immunoassays with specific antibodies offer higher sensitivity than do bioassays with indicator strains in the detection and quantification of several bacteriocins. Here we present the purification of lacticin RM and the production of specific polyclonal antibodies to a synthetic peptide resembling an internal fragment of the mature bacteriocin. The specificity and sensitivity of the generated polyclonal antibodies were evaluated in various immunoassays. The detection limits of lacticin RM were found to be 1.9, 0.16, and 0.18 micro g ml(-1) for Western blot, immuno-dot blot, and noncompetitive indirect enzyme-linked immunosorbent assays, respectively. Immunoassay sensitivities were 12.5-fold higher than that of the agar diffusion test (ADT). The production of lacticin RM showed temperature dependency, with 3, 4.2, 12.7, 28.9, 37.8, and 12 micro g ml(-1) at 37, 30, 20, 15, 10, and 4 degrees C, respectively. Temperature-stability analysis demonstrated that lacticin RM is sensitive to mild temperature, but the loss of activity does not seem to result from protein degradation. Tween 80 increased the concentration of lacticin RM eightfold and probably affected the results of the ADT either by enhancing the activity of lacticin RM or by increasing the sensitivity of the indicator strain. The use of antibodies for the specific detection and quantification of lacticin RM can expand our knowledge of its production and stability, with important implications for further investigation and future application.

Influence of pH drop on both nisin and pediocin production by Lactococcus lactis and Pediococcus acidilactici

AIMS

To develop a kinetic model for describing the specific effect of pH drop on nisin and pediocin production in whey.

METHODS AND RESULTS

The effect of pH drop on both bacteriocin productions was tested in non-buffered whey and whey buffered at initial pH 6.3 with 0.03, 0.10 and 0.25 mol l-1 of potassium hydrogen phthalate-NaOH. An accurate description of the experimental data of nisin and pediocin obtained at different pH drops is obtained with the proposed model.

CONCLUSIONS

The proposed model was able to typify both bacteriocins as pH-dependent primary metabolites.

SIGNIFICANCE AND IMPACT OF THE STUDY

The decisive role of pH drop for bacteriocin production on whey was demonstrated and modelled. This study contributes to a better understanding of underlying metabolic regulatory mechanisms, which could facilitate the optimization of bacteriocin production for upscaling.

[Bacteriocins: criteria, classification, characteristics, methods of detection]

The review on bacteriocins of Gram negative and Gram positive bacteria. Criteria making it possible to regard antagonistic substances as bateriocins or bacteriocin-like substances and on their classification are presented. Examples of bacteriocins naming depending on the taxonomic position of the producer culture are given. Information on the physico-chemical and biological properties of bacteriocins and their purification is presented as well as on detection tools of bacteriocins in microorganisms and evaluation of the producer activity of the bacteriological culture.

Partial characterization of bacteriocins produced by environmental strain Enterococcus faecium EK13

AIMS

The partial characterization of bacteriocins produced by an environmental strain Enterococcus faecium EK13, isolated from cattle dung water.

METHODS AND RESULTS

A bacteriocin was partially purified by ammonium sulphate precipitation, followed by a SP-Sepharose column, reverse-phase chromatography and N-terminal region sequenced. The anti-microbial substance produced was found to be a heat-stable polypeptide with molecular mass 4.83 kDa, which was determined by N-terminal amino acid sequencing to be enterocin A. A second substance was specified by PCR as enterocin P. Bacteriocins were stable at 4 and -20 degrees C for long storage periods. The optimum of bacteriocin production was observed in the range of pH 5.0-6.5 at 30 and 37 degrees C. The most active substances are produced by strain EK13 in logarithmic growth phase and bacteriocins are produced after 1 h of fermentation. The highest activity detected in fermentation experiments was 51 200 AU ml(-1) and the most sensitive indicator strain was found to be Listeria innocua LMG 13568. Differences in bacteriocin activity against two indicators could be explained by more than one type of enterocin production by strain EK13, or with different mode of action or in different sensitivity of strains.

CONCLUSION

Enterococcus faecium strain EK13 isolated from cattle dung water produces two bacteriocins, enterocin A and P, with an inhibitory effect against the strain of the genera Enterococcus, Leuconostoc, Lactobacillus, Streptococcus, Staphylococcus, Bacillus and Listeria (in different origin).

SIGNIFICANCE AND IMPACT OF THE STUDY

Enterococcus faecium EK13 environmental strain is a new producer of enterocin A and P. The E. faecium EK13, isolated from cattle dung water, is presented with the further aim to utilize it for waste treatment by biotechnological processes.

Characterization of Lactobacillus plantarum from wine must by PCR species-specific and RAPD-PCR

AIMS

Physiological and molecular analysis such as PCR species-specific and randomly amplified polymorphic PCR (RAPD-PCR) have been used for typing of Lactobacillus plantarum strains from typical wine must.

METHODS AND RESULTS

Phenotypic tests such as API 50CH and evaluation of D-L-lactate production from glucose were used to perform a preliminary characterization of lactobacilli. Furthermore, 18 strains of lactobacilli were analyzed by PCR species-specific oligonucleotides based on short sequences of the recA gene.

CONCLUSIONS

Four strains were identified as belonging to the L. plantarum species and were further analysed by RAPD-PCR. The RAPD-PCR profiles were similar in all strains that had positive results for species-specific PCR, suggesting that the four L. plantarum strains were closely related.

SIGNIFICANCE AND IMPACT OF THE STUDY

Using PCR species-specific as a preliminary screening test and then RAPD-PCR can be as considered the most reliable method of performing a rapid and correct typing of L. plantarum from wine must.

[Detection of biologically active substances with antagonistic and stimulating activity in Spirulina platensis]

The results of studies on the detection of biologically active substances (BAS) in biomass dilutions and culture fluid of Spirulina platensi and algae (Chlorella, Fucus, Laminaria) by the agar diffusion method are presented. After the sterilization of the solutions with chloroform (CF) a substance with lysozyme-like activity and 2 substances with antagonistic activity deep in agar and on its surface were detected with the use of the micrococcal indicator strain. After CF treatment, depending on the concentration of S. platensis strains, a compound stimulating the growth of bacteria and sensitive to heat treatment was detected. BAS were also detected with the use of other indicator cultures.

The bacteriocins of ruminal bacteria and their potential as an alternative to antibiotics

Beef cattle have been fed ionophores and other antibiotics for more than 20 years to decrease ruminal fermentation losses (e.g methane and ammonia) and increase feed efficiency, and these improvements have been explained by an inhibition of gram-positive ruminal bacteria. Ionophores are not used to treat human disease, but there has been an increased perception that antibiotics should not be used as feed additives. Some bacteria produce small peptides (bacteriocins) that inhibit gram-positive bacteria. In vitro experiments indicated that the bacteriocin, nisin, and the ionophore, monensin, had similar effects on ruminal fermentation. However, preliminary results indicated that mixed ruminal bacteria degraded nisin, and the ruminal bacterium, Streptococcus bovis, became highly nisin-resistant. A variety of ruminal bacteria produce bacteriocins, and bacteriocin production has, in some cases, been correlated with changes in ruminal ecology. Some ruminal bacteriocins are as potent as nisin in vitro, and resistance can be circumvented. Based on these results, ruminal bacteriocins may provide an alternative to antibiotics in cattle rations.

Purification and biological characterization of halocin H1 from Haloferax mediterranei M2a

The production of halocins, bacteriocin-like proteins of ecological significance, is a frequent characteristic of species from the family Halobacteriaceae. Halocin H1, produced by Haloferax mediterranei strain M2a, is a single 31-kDa polypeptide. Its purification was achieved by combining two chromatographic systems: Sepharose 4B linked to bacitracin followed by hydroxylapatite Bio-gel HTP. Halocin H1 required concentrations of NaCl higher than 1.5 M to maintain its activity. Haoarchaeal strains showed a differential degree of sensitivity to the action of this halocin.

Selection of bacteriocin producer strains of lactic acid bacteria from a dairy environment

Two strains showing bacteriocin production were selected from a total of 206 lactic acid bacteria isolated from samples of milk, milk serum, whey and homemade cheeses in Southern Cordoba, Argentina. This property was detected by means of well diffusion assays. The strains were identified as Enterococcus hirae and Enterococcus durans. The protein nature of those substances was proved by showing their sensitivity to type IV and XXV proteases, papaine, trypsin, pepsin and K proteinase. The bacteriocins inhibited the growth of Listeria monocytogenes, Bacillus cereus, Clostridium perfringes and two strains of Staphylococcus aureus, an A-enterotoxin and a B-enterotoxin producers. All of these bacteria are common pathogens usually associated with food borne diseases (ETA). These lactic acid bacteria or their bacteriocins could be suitable candidates for food preservation and specially useful in the our regional dairy industry.

Luminescent method for the detection of antibacterial activities

A new rapid and sensitive method for the detection of antibacterial activities was based on luminescent indicator strains. Listeria innocua 8811 and Enterococcus faecalis 32 were transformed with plasmid carrying bacterial luciferase genes. Subsequent strains became capable to emit light during the exponential growth phase. The addition of bacteriocin containing culture supernatants to such cultures induced a drop of their light emission which was correlated to the combined antibacterial activity of acid stress and bacteriocin. The detection of antagonistic activity is independent of its mode of action, i.e. bactericidal or bacteriostatic. This method allowed to directly visualize the antagonistic activity of bacteriocin producer strains toward target strains in coculture experiments. However, a control co-culture with non-producing bacteriocin mutant was necessary in order to distinguish between nutrients competition and bacteriocin activity. Finally, five class IIa bacteriocins were purified from culture supernatants of eight strains detected in 3 days from a 120 lactic acid bacteria collection.

Implantation of bacteria from human pulpal necrosis and translocation from root canals in gnotobiotic mice

The aim of this study was to determine whether microorganisms recovered from infected human root canals were able to survive and translocate to a local lymph node when experimentally inoculated into the root canal system of germ-free mice. The microorganisms isolated from two patients with pulpal necrosis were inoculated in two groups of experimental animals; group I (Gemella morbillorum) and group II (Bifidobacterium adolescentis, Fusobacterium nucleatum, and Clostridium butyricum). G. morbillorum showed the highest frequency of colonization and translocation to the draining lymph node. In group II only F. nucleatum and C. butyricum colonized and translocated when inoculated in tri-association. When the bacteria from group II were inoculated in monoinfection all three species colonized the root canal of germ-free mice and translocated to the draining lymph node, but with different frequencies. We conclude that selective mechanisms occur in which some bacterial species are fit to survive, multiply, and translocate in the germ-free mouse model.

An analysis of bacteriocins produced by lactic acid bacteria isolated from malted barley

AIMS

The aim of this study was to perform a detailed characterization of bacteriocins produced by lactic acid bacteria (LAB) isolated from malted barley.

METHODS AND RESULTS

Bacteriocin activities produced by eight LAB, isolated from various types of malted barley, were purified to homogeneity by ammonium sulphate precipitation, cation exchange, hydrophobic interaction and reverse-phase liquid chromatography. Molecular mass analysis and N-terminal amino acid sequencing of the purified bacteriocins showed that four non-identical Lactobacillus sakei strains produced sakacin P, while four Leuconostoc mesenteroides strains were shown to produce bacteriocins highly similar or identical to leucocin A, leucocin C or mesenterocin Y105. Two of these bacteriocin-producing strains, Lb. sakei 5 and Leuc. mesenteroides 6, were shown to produce more than one bacteriocin. Lactobacillus sakei 5 produced sakacin P as well as two novel bacteriocins, which were termed sakacin 5X and sakacin 5T. The inhibitory spectrum of each purified bacteriocin was analysed and demonstrated that sakacin 5X was capable of inhibiting the widest range of beer spoilage organisms.

CONCLUSION

All bacteriocins purified in this study were class II bacteriocins. Two of the bacteriocins have not been described previously in the literature while the remaining purified bacteriocins have been isolated from environments other than malted barley.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study represents a thorough analysis of bacteriocin-producing LAB from malt and demonstrates, for the first time, the variety of previously identified and novel inhibitory peptides produced by isolates from this environment. It also highlights the potential of these LAB cultures to be used as biological controlling agents in the brewing industry.

Detection of the bacteriocin propionicin PLG-1 with polyvalent anti-PLG-1 antiserum

Polyclonal antibodies against the bacteriocin propionicin PLG-1 were produced in rabbits at high titer (256,000 to 512,000, as determined by indirect enzyme-linked immunosorbent assay [ELISA]). Anti-PLG-1 antiserum neutralized the antimicrobial activity of PLG-1 preparations in a well diffusion assay. Cross-reacting protein was detected using an indirect ELISA of the culture supernatant from a fed-batch fermentation of the producer strain Propionibacterium thoenii P127 within the first 24 h of incubation, but bacteriocin activity was not detected in the same culture until 217 h of incubation. Culture supernatants from 156 strains of classical dairy propionibacteria were tested by indirect ELISA at 5 and 12 days of incubation for production of cross-reacting protein and by well diffusion assay for bacteriocin activity. Cross-reacting protein was detected in 52 strains: all of the tested strains of P. thoenii, most of the strains of Propionibacterium jensenii, and a minority of the Propionibacterium acidipropionici and Propionibacterium freudenreichii strains. Of these 52 strains, only 4 strains of P. thoenii showed bacteriocin activity in a well diffusion assay. Eight bacteriocin-negative mutants of strain P127 were negative in both ELISA and well diffusion assays. Western blot analysis showed that three protein bands bound anti-PLG-1 antibodies in culture supernatants: a 9.1-kDa band that is assumed to be the PLG-1 monomer and 16.2- and 27.5-kDa bands that may be precursors, multimers, or complexes of PLG-1.

[Bactericidal properties of hemo-cytolysin from Vibrio cholerae non O1 P-11702 strain in a panel of indicator cultures for detection of vibriocins]

The influence of the preparation of hemo-cytolysin, obtained from V. cholerae non O1 strain P-11702 and inducing lysis of both red blood cells and V. cholerae cultures using a panel of indicator cultures for the detection of vibriocins, was studied. The set of indicator cultures contained 2 Shigella flexneri strains, 1 S. dysenteriae strain, 3 S. sonnei strains, 3 Escherichia coli strains and 2 V. cholerae strains, one of them being atypical. Hemo-cytolysin exhibited lytic activity with respect to S. dysenteriae, S. sonnei strains and 1 V. cholerae strain. i.e. to 4 out of 11 indicator strains. V. cholerae atypical strain proved to be resistant to the preparation in contrast to 33 V. cholerae typical strains, studied previously.

Halocins: are they involved in the competition between halobacteria in saltern ponds?

Many representatives of the family Halobacteriaceae ("halobacteria") excrete halophilic bacteriocins (halocins) that inhibit the growth of other halobacteria. In spite of the fact that halocin production is widespread among the Halobacteriaceae, no information is available on their ecological significance. To test whether halocins may play a role in the interspecies competition between different types of halobacteria in saltern crystallizer ponds inhabited by dense communities of these red halophiles, we assayed for halocins active against a variety of halobacteria in salterns from different locations worldwide. Detection of halocin activity was based on the inhibition of growth of indicator organisms on agar plates, the decreased incorporation of radiolabeled substrates, and microscopic examinations. No halocin activity was detected in any of the brines examined, in spite of the fact that halocin production was demonstrated in cultures of most microorganisms isolated from these brines. Thus, the contribution of halocins in the competition between different halobacteria in hypersaline aquatic environments is probably negligible.